Blood vessels are exposed to cyclic stretch and shear stress due to blood pressure and flow. These hemodynamic forces regulate the remodeling of vascular cells (e.g., alignment, migration, proliferation, and apoptosis) during growth, development, and adaptation to physiological and pathological conditions. Studies on cultured cells in flow and stretch systems in vitro have advanced the knowledge of how different types of mechanical forces modulate the functions and remodeling of vascular cells. Steady or pulsatile shear stress (with a significant forward component) and uniaxial stretch (with a net direction) have been shown to cause alignment of cytoskeletal fibers, enhancement of cell migration, and inhibition of cell proliferation and apoptosis, with the ensuing tendency to protect against atherogenesis. In contrast, reciprocating shear or disturbed flow (with little forward component) and biaxial stretch tend to have opposite effects. Our Hypothesis is that different types of externally applied mechanical stimuli cause distinct changes of intracellular stress/strain, in terms of its spatial distribution and temporal characteristics, to result in differential alterations in molecular signaling and cellular functions. Pursuant to this hypothesis, our proposed research is designed to elucidate how the various types of mechanical forces are transmitted into ECs to alter their intracellular stress/strain, molecular signaling, and cellular functions. Four Specific Aims are proposed: 1) To establish the effects of mechanical forces on stress/strain distribution in and around the ECs by using a combination of experimental and theoretical approaches. We will determine the intracellular stress/strain by tracking fluorescently labeled molecules and particles; map the traction force exerted by the cell on the matrix; and assess the roles of cell junctions. 2) To elucidate the mechanisms by which mechanical forces modulate EC alignment and migration, with an emphasis on the spatial and temporal signaling events of focal adhesion (FA) proteins and Rho small GTPases by using FRET. We will also use mutant constructs and cells to determine the roles of these signaling molecules and junction proteins in EC migration and alignment. 3) To elucidate the mechanisms by which mechanical forces modulate EC proliferation and apoptosis by assessing the roles of KLF family molecules, as well as FA proteins and small GTPases. 4) To establish the mechanisms by which mechanical forces modulate EC alignment, proliferation and survival in vessels in vivo at aortic arch, abdominal aorta and branch points, and in aorta subjected to local constriction. The findings will advance our fundamental knowledge on mechanotransduction and remodeling, thus providing the mechanistic basis for the development of novel approaches for diagnosis and treatment of cardiovascular disorders, such as atherosclerosis, hypertension, and endothelial injury following vascular interventions, as well as diseases in other organ systems. [unreadable] [unreadable]